Reaction is NaHCO3 + HCL = H2CO3 + NaCl
the ratios are 1:1
the 8 moles of HCl are in excess
so if you use 4 moles of NaHCO3 then you will obtain 4 moles of carbonic acid
hope that helps
The third answer is the one you want. You have to have an adjustable density. All other things being equal, if the tanks you use for holding just water when filled with water will let the sub sink, because the sub is made of a dense metal like iron or steel.
If on the other hand you fill these tanks with air, the net density will be below one and the sub will rise.
Isotopes of carbon or any element
Answer: This was because the experiment showed that a substance could emit radiation even while it was not exposed to light.